When glycofurol was used as a solvent for hexobarbital or zoxazolamine, we observed a marked increase in their pharmacological actions based on measurement of sleeping times and paralysis times. Glycofural not only increased the rate of absorption, but decreased the average body clearance of hexobarbital and zoxazolamine. In addition, glycofural inhibited in vitro hepatic microsomal metabolism. In contrast, when glycofurol was administered in multiple doses (1 ml/kg ip twice a day for 4 days), it markedly decreased the sleeping and paralysis times of hexobarbital and zoxazolamine, suggesting that glycofural induces the mixed function oxidase system. Indeed, the repeated doses of glycofurol increased significantly the amounts of cytochrome P-450, cytochrome b5, NADPH cytochrome c reductase, and also the activities of ethylmorphine N-demethylase and benzopyrene hydroxylase. The nature of induction by glycofurol resembles somewhat the induction of phenobarbital, but its exact mechanism of induction remain to be elucidated.